Small-Molecule Anion Recognition by a Shape-Responsive Bowl-Type Dodecavanadate.

A dodecavanadate, [V12 O32 ]4- , is an inorganic bowl-type host with a cavity entrance with a diameter of 4.4 Å in the optimized structure. Linear, bent, and trigonal planar anions are tested as guest anions and the formation of host-guest complexes, [V12 O32 (X)]5- (X=CN- , OCN- , NO2- , NO3- , HCO2- , and CH3 CO2- ), were confirmed by X-ray crystallographic analyses and a 51 V NMR spectroscopy study. The degree of distortion of the bowl from a regular to an oval shape depends on the type of guest anion. In 51 V NMR spectroscopy, all chemical shifts of the host-guest complexes are clearly shifted after guest incorporation. The incorporation reaction rates for OCN- , NO2- , HCO2- , and CH3 CO2- are much larger than those of NO3- and halides. The incorporated nonspherical molecular anions in the dodecavanadate host are easily dissociated or exchanged for other anions, whereas spherical halides in the host are preserved without dissociation, even in the presence of the tested anions.